text/template: add lock for Template.tmpl to fix data race

This adds a new lock protecting "tmpl".

This is a copy of https://golang.org/cl/257817 by Andreas Fleig,
updated for current tip, and updated to start running the
html/template TestEscapeRace test.

Thanks to @bep for providing the test case.

Fixes #39807

Change-Id: Ic8874484290283a49116812eeaffb8608346dc70
Reviewed-on: https://go-review.googlesource.com/c/go/+/316669
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/src/text/template/exec_test.go b/src/text/template/exec_test.go
index 255b111b34..e73fce4fa8 100644
--- a/src/text/template/exec_test.go
+++ b/src/text/template/exec_test.go
@@ -12,6 +12,7 @@ import (
 	"io"
 	"reflect"
 	"strings"
+	"sync"
 	"testing"
 )
 
@@ -1732,3 +1733,40 @@ func TestIssue43065(t *testing.T) {
 		t.Errorf("%s", err)
 	}
 }
+
+// Issue 39807: data race in html/template & text/template
+func TestIssue39807(t *testing.T) {
+	var wg sync.WaitGroup
+
+	tplFoo, err := New("foo").Parse(`{{ template "bar" . }}`)
+	if err != nil {
+		t.Error(err)
+	}
+
+	tplBar, err := New("bar").Parse("bar")
+	if err != nil {
+		t.Error(err)
+	}
+
+	gofuncs := 10
+	numTemplates := 10
+
+	for i := 1; i <= gofuncs; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for j := 0; j < numTemplates; j++ {
+				_, err := tplFoo.AddParseTree(tplBar.Name(), tplBar.Tree)
+				if err != nil {
+					t.Error(err)
+				}
+				err = tplFoo.Execute(io.Discard, nil)
+				if err != nil {
+					t.Error(err)
+				}
+			}
+		}()
+	}
+
+	wg.Wait()
+}